This study will examine whether environmental asbestos deposits in California are associated with increased rates of mesothelioma, a rare cancer of the pleura and peritoneum that occurs almost solely as a result of asbestos exposure. The project brings together a multidisciplinary team to address geologic occurrence of asbestos in California, potential human exposure based on population patterns and known occupational exposures, and epidemiologic characteristics of disease in the state. The study will provide the ability to assess age-, race- and sex- adjusted mesothelioma rates in relation to asbestiform type and location as determined by geographic mapping. Previous epidemiological studies of asbestos-induced malignancy have focused primarily on occupation asbestos exposures. Studies in other countries have documented mesotheliomas due to environmental asbestos exposure, but there has been little research on this in the U.S. Information on mesothelioma cases from 1988-96 will be obtained from the California Cancer Registry, which maintains a database of all cancer cases in the state. The analysis will examine the distribution of age-, sex- and race-adjusted county-specific mesothelioma rates to assess whether populations in counties with large concentrations of environmental asbestos have a higher rate of mesothelioma than populations in counties with little or no endogenous asbestos. The location and distribution of amphibole and serpentine asbestos deposits in California will be determined by a review of existing geological surveys and publications, along with case studies of the occurrence of tremolite asbestos. This information will be combined with measures of human interaction with environmental asbestos, such as development, mining, and population density, to determine potential human exposure to environmental asbestos by county. Lastly, this project will plan a case-control study to more rigorously test the hypothesis that mesothelioma in California is independently associated with environmental asbestos exposure. The proposed project will be the first study to test the association of environmental asbestos and adjusted county- specific rates of mesothelioma. It is particularly strengthened by a comprehensive analysis of environmental tremolite and asbestos in California to be conducted by Dr. Howard Day, Department of Geology, UC Davis. This study is particularly important and timely because of the increasing population in the state living in asbestos-containing areas. California represents a unique location for these studies because of the statewide tumor registry, the largest tumor registry in the world.